the earth will absorb it but the scent even though you won't smell it the dog may still be able to. How old is the dog and is it housebroken. If not then it should not have been left unsupervised. If he has accidents in the house you must retrain him as if he were a puppy. Which means crated or leashed to you so he doesn't have the opportunity to pee in the house. A bichon is a smart little dog and easy to train. If you think he's been abused you need to spend a lot of time with him to gain his confidence, once he feels comfortable with you then you can start training and working with him. They learn quickly so it won't be much of a stretch to see him well trained in little time.
he is your friend and protector, he will love you unconditionally, you owe it to him to be worthy of such devotion